A compound of above formula (I) is generally called "Diclofenac" and has anti-inflammatory, analgetic and anti-pyretic effects as disclosed in Japanese Pat. No. 23418/1967.
Processes for production of the compound (I) and salts thereof have been disclosed in Japanese Pat. Nos. 23418/1967, 27573/1969, 11295/1970 and 20469/1977. However, those known processes have drawbacks in that they comprise many steps and that yield of the intended product after completion of the all steps is poor. The processes are, therefore, industrially unsatisfactory.
Studies were already made for the purpose of simplifying the steps, resulting in obtaining the intended compound (I) by reacting o-bromo-, o-iodophenylacetic acid or a salt thereof with 2,6-dichloroaniline or an N-substituted derivative thereof in one step as disclosed in Japanese Patent Public Disclosure Nos. 71439/1977, 73749/1979 and 72152/1980 and Japanese Pat. No. 374/1980.
However, the process for production of the intended compound (I) by using o-chlorophenylacetic acid in place of o-bromo- or o-iodophenylacetic acid has not been completed yet owing to the lower reactivity of the chlorine atom in substitution with aromatic amines.
On the other hand, E. D. Bergmann and Th. Bille-Same [Bull. Soc. Chim. Fr., pp. 1090-1091 (1968)] reported that the reaction of o-chlorophenylacetic acid with aniline gave N-phenyloxyindole, biphenyl ether-2,2'-diacetic acid or the like.
This fact suggests that, in case o-chlorophenylacetic acid is used for production of the intended compound (I), the reaction may proceed in a different way from the reaction of o-bromo- or o-iodophenylacetic acid with 2,6-dichloroaniline disclosed in said Japanese Pat. No. 374/1980.
Thus, for production of the intended compound (I) from o-chlorophenylacetic acid and 2,6-dichloroaniline, it has been demanded to improve the selectivity of the reaction.